000
AXUS76 KMTR 121701
DGTMTR
CAC001-013-041-053-055-069-075-081-085-087-097-122300-
DROUGHT INFORMATION STATEMENT
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
901 AM PST THU FEB 12 2015
...DROUGHT CONDITIONS IMPROVE IN COASTAL NORTHERN CALIFORNIA...
A MODEST ATMOSPHERIC RIVER EVENT LATE LAST WEEK AND WEEKEND
DELIVERED SIGNIFICANT AMOUNTS OF RAINFALL TO MUCH OF NORTHERN
CALIFORNIA. AREAS WHICH RECEIVED THE MOST RAINFALL TENDED TO BE IN
NORTHERN CALIFORNIA NORTH OF SAN FRANCISCO BAY. HERE...STORM TOTAL
RAINFALL EXCEEDED 10 INCHES IN MANY LOCATIONS...AND REACHED AS
HIGH AS 15 INCHES OR SLIGHTLY MORE IN THE MOST PROLIFIC SPOTS.
EVEN AREAS IN THE NORTH BAY MOUNTAINS...WITHIN THE AUSTIN CREEK
AND GUALALA RIVER BASINS...RECEIVED UP TO 14 INCHES OF RAIN. WHILE
THE GENEROUS PRECIPITATION WAS MORE WIDESPREAD IN NORTHWESTERN
CALIFORNIA...RAINFALL AMOUNTS ABOVE 5 INCHES TOTAL WERE MORE
LOCALIZED IN THE SF BAY AREA AND THE CENTRAL COAST. HERE...THE
STORM SYSTEM WAS STRONGLY OROGRAPHICALLY CONTROLLED...MEANING THAT
COASTAL MOUNTAINS WERE PARTICULARLY EFFECTIVE IN WRINGING OUT
MOISTURE FROM THE STORM SYSTEM MOVING EAST. THIS MEANT THAT
COASTAL MOUNTAINS RANGES LIKE THE SANTA CRUZ AND SANTA LUCIA
RANGES RECEIVED 5 INCHES OR MORE STORM TOTAL PRECIPITATION DURING
THE EVENT...WHILE LOWER ELEVATION AREAS ALONG THE COAST AND INLAND
VALLEYS RECEIVED FAR LESS. RAINFALL TOTALS IN THESE COASTAL
MOUNTAIN RANGES WERE GENERALLY IN EXCESS OF 5-6 INCHES, AND
REACHED UP TO 10 INCHES IN SOME HIGH ELEVATION SPOTS (SCHULTIES...MOUNT
UMUNHUM...AND THREE PEAKS...TO NAME A FEW). THE MONTEREY
PENINSULA...PAJARO VALLEY...AND SANTA CLARA VALLEY...HOWEVER...ONLY
RECEIVED 3 INCHES OR TYPICALLY FAR LESS RAIN. HERE AT OUR OFFICE
IN MONTEREY...FOR EXAMPLE...ONLY 0.7 INCHES FELL. OTHER AREAS LIKE
THE SALINAS VALLEY...THE EAST BAY...AND SAN BENITO COUNTY RECEIVED
SIMILARLY SCANT AMOUNTS OF RAIN IN GENERAL.
BECAUSE OF THE RECENT RAINS...DROUGHT CONDITIONS HAVE IMPROVED
SLIGHTLY IN COASTAL AREAS OF NORTHERN AND CENTRAL CALIFORNIA. IN
PARTICULAR...THE DROUGHT DESIGNATION OF D3 (EXTREME DROUGHT) HAS
BEEN LOCALLY IMPROVED TO D2 (SEVERE DROUGHT) IN SONOMA
COUNTY...EXTREME WESTERN NAPA COUNTY...THE CORE OF THE SANTA CRUZ
MOUNTAINS IN SANTA CRUZ AND SANTA CLARA COUNTIES...AND THE
NORTHERN CORE OF THE SANTA LUCIA RANGE IN MONTEREY COUNTY. THESE
CHANGES REFLECT THE EFFECT THAT GENEROUS RAINFALL TOTALS HAVE HAD
ON LOCAL MOISTURE STORES...PARTICULARLY SMALL LOCAL
RESERVOIRS...GROUNDWATER SYSTEMS...AND CREEKS...RIVERS...AND
SPRINGS. LARGER RESERVOIRS SERVING SONOMA COUNTY...SUCH AS LAKE
SONOMA AND LAKE MENDOCINO...ARE AT 86 AND 96 PERCENT OF THEIR
RESPECTIVE WATER SUPPLY POOLS AND ARE CONTINUING TO FILL IN
RESPONSE TO ELEVATED LEVELS IN TRIBUTARY CREEKS FEEDING THEM. IN
GAGED STREAMS...RECEDING LIMBS OF HYDROGRAPHS HAVE LEVELED OFF AT
BASEFLOWS INDICATIVE OF SATURATED WATERSHEDS. SOME ARE STILL
RECEDING FROM THE STORM RUNOFF AND HAVE NOT YET RETURNED TO BASEFLOW.
AS THE USDM MAP ILLUSTRATES
(WWW.DROUGHTMONITOR.UNL.EDU/HOME/STATEDROUGHTMONITOR.ASPX?CA)...THE
IMPROVEMENTS ARE LIMITED TO THE NORTHWESTERN PORTIONS OF THE
STATE. NO IMPROVEMENTS HAVE BEEN MADE IN CENTRAL VALLEY OR SIERRAN
LOCATIONS (AND ELSEWHERE). THIS REFLECTS TWO MAIN CONDITIONS. 1)
THE RECENT RAINS WERE VERY WARM...SO VERY LITTLE SNOWPACK
CONTRIBUTIONS WERE MADE IN THE SIERRA. 2) RAINFALL AMOUNTS WERE
MUCH HIGHER IN NORTHWESTERN COASTAL LOCATIONS AND NOT NEARLY AS
HIGH IN THE CENTRAL VALLEY OR THE SIERRA. THE ADDITIONAL RUNOFF
THAT IS BEING PROVIDED TO LARGER CALIFORNIA RESERVOIRS ALONG THE
WESTERN SLOPE OF THE SIERRA IS HELPING TO FILL THESE RESERVOIRS IN
SMALL TO MODEST AMOUNTS...BUT THE MEAGER SNOWPACK FOLLOWING THE
STORM SYSTEM OF ABOUT 27% OF AVERAGE MEANS THAT THE IMPROVEMENTS
WILL BE HIGHLY TRANSIENT WHERE THEY DO OCCUR.
CURRENT FORECASTS ARE UNCERTAIN ON HOW MUCH RAIN WE MAY RECEIVE
FOR THE REMAINDER OF THE WET SEASON. NO RAIN IS YET FORECAST IN
THE NEXT 7 TO 10 DAYS. IF DRY CONDITIONS SET IN AGAIN AS THEY DID
THROUGH JANUARY...THE IMPROVEMENTS IN DROUGHT CONDITIONS ALONG THE
COAST MAY ALSO BE SHORT-LIVED. EXPECT QUICK RETROGRADATION TO D3
IF A MONTH OR MORE OF DRYNESS FOLLOWS. IT IS LIKELY THAT ONLY
COPIOUS AMOUNTS OF PROTRACTED RAINFALL THROUGH THE REMAINDER OF
THE WET SEASON COULD MAKE ANY ADDITIONAL IMPROVEMENTS IN DROUGHT
BEFORE THE DRY SEASON BEGINS. THIS MEANS IT IS VERY LIKELY THAT
THE DROUGHT CONDITIONS REFLECTED STATEWIDE WILL NOT IMPROVE
BEYOND WHAT IS CURRENTLY DEPICTED...UNLESS GENEROUS RAINFALL IS
DELIVERED TO CALIFORNIA.
THE CURRENT IMPROVEMENTS WILL NOT LIKELY LEAD TO CHANGES IN WATER
SUPPLY MANAGEMENT...PARTICULARLY WITH RESPECT TO WATER RATIONING
AND RESTRICTIONS IN USAGE. THE IMPROVEMENTS ARE ALSO NOT AN
INVITATION TO SLACKEN CONSERVATION MEASURES BY HOMEOWNERS OR
OTHERWISE. IN FACT...WATER MANAGERS ACROSS THE STATE ARE
CONTINUING TO STRONGLY URGE CONSERVATION AND PRUDENT USAGE OF
WATER. IMPACTS OF THE DROUGHT ARE STILL BEING FELT STATEWIDE...AND
IMPROVEMENTS IN DROUGHT CONDITIONS AND REDUCED IMPACT IS ONLY
HIGHLY LOCALIZED...AND IS LIKELY SHORT-LIVED...AS DESCRIBED ABOVE.
AN UPDATE TO THIS DROUGHT INFORMATION STATEMENT WILL BE ISSUED IN
RESPONSE TO CHANGES IN CONDITIONS AND DROUGHT MONITOR STATUS IN
THE SF/MONTEREY BAY AREA.
$$
STRUDLEY
WEATHER.GOV/SANFRANCISCO